Gasifiers, such as those employing fluidized beds, have been used to convert carbonaceous materials into a product gas. The objective in gasification is to maximize the conversion of feedstock into syngas i.e., H2 and CO. This requires that either the formation of condensables or tars and light hydrocarbons is minimized or that these are converted in-situ. Many investigators have developed catalysts to crack tars and/or reform hydrocarbons in steam reforming, autothermal reforming and partial oxidation modes of reactor operation. The key performance targets are conversion, yield, selectivity and activity and the challenge is to maintain performance with negligible or minimal loss of activity. The potential factors that can lead to catalyst deactivation or degradation are: attrition or decrepitation of the particle or catalyst layer, sintering, agglomeration, coke formation and poisoning due to feedstock impurities (H2S, COS, HC1, NH3, HCN, etc.). Some recent reviews include:
Gerber, M. A., “Review of Novel Catalysts for Biomass Tar cracking and methane Reforming”, Pacific Northwest National Laboratory Report PNNL-16950, Oct. 2007.
Fang, H., Haibin, L., and Zengli, Z., “Advancements in Development of Chemical-Looping Combustion: A Review’, Intl. J. Ch. E., Volume 2009 (2009), Article ID 710515.
Kolb, G., “Fuel Processing: for fuel cells”, Technology & Engineering, 2008, 424 pages.
Advanced catalysts which can operate under the adverse conditions of gasification chambers are described in the following U.S. published patent applications, whose contents are incorporated by reference: US20080041766A1, US20070116639A1 and US20090209412A1.
US20080041766A1 to Giroux et al. teaches a method of reforming a sulfur containing hydrocarbon involves contacting the sulfur containing hydrocarbon with a sulfur tolerant catalyst containing a non-sulfating carrier and one or more of a sulfur tolerant precious metal and a non-precious metal compound so that the sulfur tolerant catalyst adsorbs at least a portion of sulfur in the sulfur containing hydrocarbon and a low sulfur reformate is collected, and contacting the sulfur tolerant catalyst with an oxygen containing gas to convert at least a portion of adsorbed sulfur to a sulfur oxide that is desorbed from the sulfur tolerant catalyst. This invention is intended to be carried out in a simple reactor or a swing reactor but not a fluidized bed.
US20070116639A1 to Lomax et al. teaches the preparation of a catalyst that can be used for the production of hydrogen from hydrocarbon fuels in steam reforming processes; the catalyst contains an active metal of, e.g., at least one of Ir, Pt and Pd, on a catalyst support of, e.g., at least one of monoclinic zirconia and an alkaline-earth metal hexaaluminate and it exhibits improved activity, stability in both air and reducing atmospheres, and sulfur tolerance. Preferred reactor type is not indicated but the application seems to suggest a packed bed or fixed bed reactor.
US20090209412A1 to Parent et al. teaches a method of preparing a steam reforming catalyst characterized by improved resistance to attrition loss when used for cracking, reforming, water gas shift and gasification reactions on feedstock in a fluidized bed reactor, comprising: fabricating the ceramic support particle, coating a ceramic support by adding an aqueous solution of a precursor salt of a metal selected from the group consisting of Ni, Pt, Pd, Ru, Rh, Cr, Co, Mn, Mg, K, La and Fe and mixtures thereof to the ceramic support and calcining the coated ceramic in air to convert the metal salts to metal oxides. This is specifically intended for fluid bed application but is made in the form of spherical particles ranging in size from 100 to 1,000 microns by agglomerating catalyst support material. Typically the un-fired agglomerates are composed of catalyst support particles with an average size in the range of 0.3 to 10 microns, preferably in the range of 0.9 to 5 microns.
Heat is required for the gasifier bed to sustain the endothermic reaction of converting the carbonaceous material into the product gas. The heat may be provided by one or more direct or indirect heat sources. In general, such heat sources consume considerable energy.